The present invention relates to an ink jet printer generally of the type disclosed in U.S. Pat. No. 3,701,998, issued Oct. 31, 1972, to Mathis. The Mathis printer includes a print head having an orifice plate defining two rows of orifices. Two rows of jet drop streams are generated from the single print head. The drop streams pass through two corresponding rows of charge rings. The rows of jet drop streams then pass on opposite sides of an electrically conductive deflection electrode which provides a static electrical deflection field for deflecting selectively drops outward from the electrode.
A pair of electrically conductive catchers are positioned outwardly of the rows of jet drop streams, each of the catchers being positioned directly opposite the deflection electrode. The catchers are formed of electrically conductive material and are electrically grounded such that a substantial electrical field is provided between the deflection electrode and each of the catchers. Charged drops from the jet drop streams are deflected outward such that they strike the catchers. Each catcher includes a vertical drop catching surface which is struck by the deflected drops. The drops then run down this surface and are ingested into a single catcher cavity, defined within the body of the catcher, via a drop ingesting slot which extends along the catcher beneath the drop catching surface.
A number of different catcher designs have been utilized in ink jet printers. U.S. Pat. No. 3,611,422, issued Oct. 5, 1971, to Rourke discloses a metal catcher which is positioned below a pair of deflection electrodes. Since deflection of selectively charged drops is accomplished by the field provided between the pair of electrodes, the catcher of Rourke need not be grounded.
U.S. Pat. No. 3,936,135 issued Feb. 3, 1976, to Duffield discloses a drop catcher structure which is mounted beneath a pair of deflection electrodes. This catcher need not be electrically grounded since it is not utilized to produce the drop deflection field. Another catcher structure is disclosed in IBM Technical Disclosure Bulletin, Vol. 19, No. 6, November 1976, "Ink Jet Gutter", Hungarter et al. The disclosed catcher structure is formed of multiple laminations of non-conductive material. The gutter is positioned beneath the portion of the printer which provides aiming of the jet drop streams.
Several other catcher designs have been utilized in printers of the type in which the catcher is positioned directly opposite the deflection electrode. One such catcher is shown in U.S. Pat. No. 3,777,307, issued Dec. 4, 1973, to Duffield and U.S. Pat. No. 3,836,914, issued Sept. 17, 1974, to Duffield. This catcher has a porous metal insert positioned along its upper surface, covering an elongated, partially evacuated cavity. It further includes a convex catching face having a lower radius of about 0.114 cm and extending rearwardly into a drop ingesting slot. The catcher defines a single internal catcher cavity into which the ink is drawn by a partial vacuum supplied to the cavity through a pair of vacuum tubes.
U.S. Pat. No. 3,813,675, issued May 28, 1974, to Steffy et al discloses a catcher having a series of facial channels for carrying away the ink deposited on the drop catching surface. The channels are aligned with the jets such that each jet has its own channel for guiding ink into a single internal catcher cavity.
U.S. Pat. No. 4,035,811, issued July 12, 1977, to Paranjpe, discloses a catcher having a substantially vertical drop catching surface and an upwardly extending drop ingesting opening defined in part by a curved surface at the bottom of the drop catching surface. Drops which strike the drop catching surface flow downward and, thereafter, upward through the opening. A bottom plate, extending along the bottom of the catcher and defining the drop ingesting opening with the curved surface, is formed from a porous material.
Various difficulties have been encountered with prior art catchers. Printers utilizing a catcher which is positioned beneath a separate drop deflecting electrode structure are disadvantageous in that the path traveled by each drop is substantially greater than is the case in a Mathis type printer. It will be appreciated that an increase in the path of the jet drops amplifies the effect of errors in the drop trajectories.
Prior art catchers used in Mathis type printers, in which the catchers are positioned directly opposite a deflection electrode, have also presented problems in operation. Such catchers have typically been formed of an electrically conductive material. As a result, ink build-up on the upper surfaces of such a catcher has, on occasion, resulted in shorting between the charge electrodes and the grounded catcher. Also, the single cavity defined within such a catcher has produced turbulent air and ink flow and uneven ingestion of ink through the drop ingesting slot. If sufficient ink builds up on the drop catching surface in the region of the slot, this ink may interfere with the trajectories of the drops which are intended to pass adjacent the catcher and strike the print receiving medium. Further, the height of the slot has been somewhat difficult to control precisely, since this slot is defined by a curved drop catching surface in conjunction with a lower plate.
Where multiple vacuum tubes have been connected to the catcher cavity from a vacuum manifold, variation in the suction provided from these tubes has also resulted in an uneven drop ingestion along the length of the slot. Finally, construction of catchers from a conductive material has been relatively difficult and expensive.
Accordingly, it is seen that there is a need for a simple, easily fabricated catcher structure, which avoids the disadvantages of prior art catchers.